The highly anticipated portrait, unveiled Wednesday at the National Press Club in Washington and in news conferences in six other cities across the globe, shows an extraordinary, “supermassive” black hole at the center of Messier 87, a gigantic galaxy about 55 million light-years away in the constellation Virgo.
The image was produced by the Event Horizon Telescope, a network of 10 radio telescopes spread across the planet and functioning as if it were a single receiver, one tuned to high-frequency radio waves. It represents a technical triumph for the scientists involved, and inaugurates a new era in the study of black holes, galaxy formation, and the laws of physics under extreme conditions.
The M87 black hole appears as a dark shadow within a doughnut-like ring of hot, glowing material.
"You’re basically looking at a supermassive black hole that’s almost the size of our solar system,” or 38 billion kilometers in diameter, said Sera Markoff, an astrophysicist at the University of Amsterdam who spoke at the Washington news conference.
Within the shadow in the image is the black hole’s event horizon — the point of no return, where the gravity becomes so extreme that nothing that enters can ever leave. At the center of the black hole, time and space become so curved upon themselves that the laws of physics break down completely.
The thrilling success of the observation was coupled with a twinge of disappointment, because the new image does not upend the scientific consensus about black holes. The distinctive doughnut shape of the black hole matches what theorists had expected. Significantly, the M87 black hole doesn’t show any sign of disobeying the physics equations of Albert Einstein’s general theory of relativity.
Science is typically an incremental enterprise with relatively few drumroll-inciting press conferences. But this was exactly that. The mere announcement of the press conferences generated days of news stories. Somehow, the historic first image of a black hole was kept under wraps for months by the Event Horizon Telescope team. Like the Mueller Report, it never leaked.
At 9:07 a.m. EDT, Shep Doeleman, the Harvard astrophysicist who directed the project, took the podium at the press club in Washington and said, “Here it is.” The simple, bold, orange-hued image flashed on the big screen behind him. Simultaneously the image appeared on the project’s web site, and quickly went viral online, with the predictable parodies and expert commentary on how much it looked like the Eye of Sauron from “Lord of the Rings.”
Doeleman said after the news conference that about 400 people associated with the project had seen the image before Wednesday. Everyone understood how important it was to keep it secret and remain united, he said.
“You have 400 people who are essentially spies. Will not break under any torture,” he said.
Markoff said she and other scientists got their first look at an early image of the M87 black hole last summer, and although it generally matched what the computer models had predicted a black hole would look like, she was still in awe.
“The impact of really seeing it for the first time, it was really surprising, kind of emotional,” she said. “I walked around with the image on my cellphone and I kept pulling it out and looking at it at random moments. And I couldn’t tell anybody."
Another team member, theoretical astrophysicist Avery Broderick of the Perimeter Institute, said he kept giving lectures on black holes but was forced to keep the image secret while his colleagues refined the data and wrote the papers about what the image signified. “Hardest thing ever,” he said. “You can tell no one.” The news conference Wednesday, he said, “is an enormous psychological relief to me.”
The image had its origins over the course of a week in April 2017, when EHT astronomers on four continents coordinated their efforts. Black holes, characterized by their extreme density, are tiny compared to other astronomical objects. Even supermassive black holes have an almost imperceptibly small profile.
The scientists decided they had two plausible targets. One is the black hole known as Sagittarius A*, at the heart of our own Milky Way galaxy, which has a mass equivalent to more than 4 million suns and resides some 25,000 light years away. The other is the black hole in M87. It’s much farther away, but also much larger, with a mass of 6.5 billion suns.
To perform the observation, the astronomers battled bad weather and glitchy electric grids. They donned oxygen tanks and climbed three-mile-high mountains to escape the interference of Earth’s atmosphere. Then they spent the two years parsing literal truckloads of data, some of which had to be shipped on hard drives from the South Pole and defrosted outside a supercomputer facility at MIT. Finally, they tested their findings against the results of a million simulations of what a black hole might look like, until at last they spotted a match.
Feryal Ozel, an astrophysicist at the University of Arizona and member of the science council for the EHT, called the result the highlight of her career.
“We are able to image one more object in the universe that … at one point people thought could not be possible,” she said. “It hits that human explorer spirit. We got another look into the unknown.”
The foundations for this discovery were laid more than 100 years ago, when Einstein published the equations that defined modern gravitational physics. General relativity, first described in 1915, explained gravity as a phenomenon created when matter warps the geometry of space and time. In turn, curved space and time (“space-time”) tells matter how to move.
Months after Einstein produced the equations for general relativity, German physicist Karl Schwarzschild calculated that if an object is dense enough, it would create what we now call a black hole. Einstein never liked the idea, but it hung around, and gradually scientists started seeing evidence that black holes really exist.
Searches of the sky showed the paths of stars being bent by a black hole’s tremendous gravity, and telescopes revealed the brilliant jets of light produced as the superheated material swirling around a black hole is splashed back into space. In 2016, scientists revealed ripples in space-time caused by black holes colliding — the first-ever detection of the phenomenon known as gravitational waves.
To capture a direct image of a supermassive black hole was a daunting technological challenge. M87 and Sagittarius A* are both so distant they would appear to Earthlings as a doughnut on the moon. To see them in any kind of detail, scientists would need a telescope as big as the planet — and, of course, no such thing existed. So in the mid-2000s, scientists began to MacGyver a telescope out of previously existing infrastructure, linking up instruments around the world to collect scores of observations, each from a slightly different perspective.
This kind of cosmic triangulation, called “very long baseline interferometry,” took years to refine. Some telescopes had to be upgraded to capture the right kinds of light. Researchers needed to install atomic clocks precise enough to match up their observations down to the microsecond. Supercomputers had to become orders of magnitude more powerful to process the mountains of data collected.
Most significant was an improvement in VLBI technology that allowed for observations in extremely high-frequency radio waves. This is the one form of light that can penetrate the hot gas around a black hole, the dusty expanses of the galaxy, and the Earth’s atmosphere, carrying an uninterrupted signal from the event horizon all the way to telescopes on Earth.
“We were inventing the methods by which we make images as we went along,” said team member Dan Marrone, an astrophysicist a the University of Arizona.
Finally, in 2017, the EHT was ready. Ozel, who helped coordinate the week of observations from the project’s makeshift command center at MIT, recalled the surge of excitement as hundreds of astronomers around the world prepared for their first night of work.
“There was an element of the unknown,” she said. Technical difficulties or bad weather at any of the eight sites could jettison a whole night of observations. Even if everything went to plan, the astronomers would be working 16 hours a night gathering data. And it would be months before anyone knew whether their work had paid off.
To Marrone, who coordinated observations in Arizona and at the South Pole from his office at the University of Arizona, “exhausting doesn’t begin to describe it.” He guessed that he slept for only three hours out of every 24.
After five nights of observing (with one rest day while heavy winds rocked the project’s Mexico telescope), the project had collected 5 billion megabytes of data — the equivalent of 960 hard drives containing 2 billion high-quality photographs.
Somewhere in that vast collection was the image of a black hole. Now the scientists had to find it. Geoffrey Crew, an astronomer at MIT who helped coordinate the data processing, compared the effort to discerning a concerto played at a piano that is missing several keys.
“If you only have a couple of notes, you don’t know what you’re listening to,” he said. “It’s trying to reconstruct the missing data based on what we know about how music works to create the song.”
Four subgroups at four laboratories around the globe were assigned to develop the image using four algorithms; none was allowed to know what the others were doing, as a form of quality control.
“If the scientific goal wasn’t so attractive and so full of potential, and if we hadn’t spent so much time working toward this goal, I think it probably would have fallen apart,” Ozel said. “The science kept us together.”
Their work isn’t done: Doeleman, the director of the project, said his team is still analyzing the data from observations of Sagittarius A*, which he described as a dynamic and exciting black hole compared to the more stately M87 black hole. It may be possible to capture short-term changes in Sagittarius A*, he said.
“Imagine if we can make a movie of a black hole instead of a still image,” he said.